Abstract

Endogenous selection is often implicated in the maintenance of stability of natural hybrid zones. Environmental conditions often vary across these zones, suggesting that local adaptation to ecological conditions could also play a role in this process. We used niche modeling to investigate these alternatives in a hybrid zone between two species of brown lemur (Eulemur rufifrons and E. cinereiceps) in southeastern Madagascar. We produced ecological niche models (ENMs) for parental and hybrid populations and compared values of niche overlap to null expectations using identity and background tests. All three taxonomic groups had nonequivalent ENMs with limited spatial overlap, supporting a role for niche divergence and local adaptation in the maintenance of this zone. However, values of niche overlap between ENMs were not greater than null expectations controlling for background environmental differences. These results could suggest that taxa in this hybrid zone inhabit portions of their environments that are more similar to their backgrounds, i.e., niche conservatism. Nevertheless, we did find evidence of niche divergence when using background tests that examined environmental variables separately. Although we could not rule out models indicating selection against hybrids, most lines of evidence were consistent with predictions for the bounded superiority model of hybrid zone stability. This study thus provides support that exogenous, environmental selection may be responsible for maintaining the hybrid zone, and may be implicated in the evolutionary divergence of these taxa.

Notes

Acknowledgments

The authors express their appreciation to Giuseppe Donati for the invitation to contribute to this special issue. The authors also thank the government of Madagascar for permission to conduct the original research reanalyzed here. The authors are grateful for the funding that contributed to the original field research: Primate Action Fund, Primate Conservation, Inc., American Society of Primatologists, National Science and Engineering Research Council of Canada, Omaha’s Henry Doorly Zoo and Aquarium, and University of Calgary. Omaha’s Henry Doorly Zoo and Aquarium Center for Conservation and Research, Madagascar Biodiversity Partnership and Madagascar Institut pour la Conservation des Ecosystèmes Tropicaux facilitated the fieldwork. The authors also thank Alison Porter for assistance with analyses. Finally, we thank three anonymous reviewers and the editor-in-chief for their helpful suggestions to improve the manuscript.

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